1. Field of the Invention
This invention relates to a method for water-repellent processing of a tip or the like of a tube and an apparatus used therefor.
In particular, this invention relates to a method and apparatus which are useful for forming a water-repellent surface on a portion of a nozzle of a metering pipette near the tip thereof, which pipette is used in chemical analyses for supplying a constant volume of a liquid sample.
2. Description of the Prior Art
Recently, dry-type clinical chemical analyses have been used widely because of the ease with which the analysis operations can be conducted, the speed with which measurements can be made and the like. In these analyses, a liquid sample to be tested for, e.g. blood or the like, is spotted on a chemical analysis slide which contains a reagent which reacts with a specific ingredient such as glucose or urea nitrogen (BUN) in the liquid sample; and then coloring, discoloring or the like which is caused by the reaction between the reagent and the specific ingredient is colorimetrically measured to determine the amount of the specific ingredient.
Conventionally, in order to spot the sample to be tested for (the liquid sample) on the chemical analysis slide, a predetermined amount of the sample is drawn into a pipette and then a circular drop of the sample is formed on a tip of the pipette so that it will come softly into contact with the center portion of the chemical analysis slide and be spotted thereon.
In such a method for spotting the sample, it is difficult to carry out analyses with a sufficient accuracy due to large differences in how individuals carry out the spotting of the sample. These differences mainly result from the fact that it is difficult to maintain a constant relationship between the position of the tip of the pipette (nozzle) and the surface of the chemical analysis slide on which the sample is spotted, and that, after the sample is drawn into the nozzle, a drop may not always form unless the liquid sample attached to the outside of the tip of the nozzle is wiped away.
One good way to eliminate the differences in the accuracy with which the liquid sample is spotted is to mount the pipette on a support and then to discharge manually or automatically the liquid sample out of the pipette. However, since the distance between the tip of the pipette and the sample-spotting surface of the chemical analysis slide is constant in this method, the drop cannot be brought into contact with the chemical slide and be spotted thereon after it has formed on the tip of the nozzle of the pipette.
The liquid sample may be whole blood, blood plasma, blood serum, dilute solutions thereof, urine, saliva, or the like which have various viscosities or the like and, accordingly, are absorbed into a liquid-receiving surface (a spreading layer in most cases) at different rates. Also, the rate at which one kind of liquid sample is absorbed into the liquid receiving surface may differ for various kinds of analysis slides which are used according to the ingredients to be detected. When the rate at which the liquid sample is discharged from the pipette is much higher than the rate at which it is absorbed into the chemical analysis slide, a part of the drop may attach itself to the circumference of the tip and remain there, and thereby an error may occur in the amount of the liquid sample spotted. Namely, the amount of the liquid sample supplied to the chemical analysis slide decreases when the drop is attached to the circumference of the tip, and the attached drop is additionally spotted on the chemical analysis slide in the next spotting operation. Thereby a positive error occurs in the amount of the liquid sample thus spotted.
In order to prevent the drop from attaching itself to the outer surface of the tube near the tip of the nozzle, it has been proposed to form only the outer surface of the tube from a water-repellent material. However, when the nozzle has such a twofold structure, the process for making the nozzle is complicated and the cost therefor increases.
Also, it is troublesome to wipe away the liquid sample attached to the outer surface of the tip of the nozzle each time the liquid sample is drawn thereinto. Such a wiping operation will be forgotten and, accordingly, an error will occur in the amount of the liquid sample unless attention is paid thereto.